The invention pertains to a method for removing ice layers and/or snow layers and/or dirt layers from the rotor blades of axial fans in cooling installations for refrigerating and/or freezing products, as well as to an apparatus for carrying out this method.
An axial fan as it is sufficiently known from the state of the art is a fluid flow engine that is equipped with a rotor, on the circumference of which rotor blades are arranged. Due to the geometry of the rotor blades, the rotating rotor is able to take in gas and pass on the gas in the direction of its rotational axis (axially) with increased pressure, wherein this is the reason why rotor blades have so-called suction sides and pressure sides.
In order to refrigerate and/or freeze products, particularly food products, it is common practice to utilize refrigerating devices, in which the products are transported through a treatment zone, wherein heat of the products is absorbed in said treatment zone by a cool atmosphere. One popular refrigerating device, for example, is a so-called tunnel froster, in which food products are brought in contact with cold gas such as, e.g., cold carbon dioxide, nitrogen or cold air and thusly refrigerated and/or frozen while they continuously move through a housing of tunnel-like design. In order to improve the heat transfer from the products to the cold atmosphere, the cold atmosphere is frequently circulated within the treatment zone with the aid of one or more fans. Part of the humidity that is admitted into the treatment zone with the products to be refrigerated or the ambient air is absorbed by the cold atmosphere and precipitated in the form of ice or snow at a different location within the refrigerating device. This effect causes the formation of ice layers or snow layers on solid surfaces, particularly also on the rotor blades of the fans. The geometries of the rotor blades in the non-icy state are optimized with respect to the output of a fan, i.e., the maximum volumetric flow rate of the cold atmosphere to be circulated by the fan. This means that deviations from the optimal geometry as they may be caused by an ice layer reduce the output and therefore lower the speed of the cold gas flowing past the products. The same effect also occurs when dirt layers are deposited on rotor blades.
The heat transfer between a solid body and a gas is highly dependent on the relative speed between the gas and the solid body: the lower the relative speed, the worse the heat transfer. Consequently, ice layers and/or dirt layers on the rotor blades of fans lead to a deterioration of the heat transfer from the products to be refrigerated to the cold atmosphere and therefore to a reduced refrigerating capacity of a refrigerating device. If the refrigerating capacity falls short of a predetermined value, it is necessary to interrupt the production of apparatuses according to the state of the art in order to open the refrigerating device and to clean the rotor blades. Ice layers and/or dirt layers deposited on rotor blades therefore significantly affect the efficiency of such refrigerating and/freezing methods.